Ring-opening polymerization from cellulose for biocomposite applications
There is an emerging interest in the development of sustainable materials with
high performance. Cellulose is promising in this regard as it is a renewable
resource with high specific properties, which can be utilized as strong
reinforcements in novel biocomposites. However, to fully exploit the potential of
cellulose, its inherent hydrophilic character has to be modified in order to
improve the compatibility and interfacial adhesion with the more hydrophobic
polymer matrices commonly used in composites.
In this study, the grafting of poly(?-caprolactone) (PCL) and poly(L-lactide)
(PLLA) from cellulose surfaces, via ring-opening polymerization (ROP) of ?-
caprolactone and L-lactide, was investigated. Both macroscopic and nano-sized
cellulose were explored, such as filter paper, microfibrillated cellulose (MFC),
MFC-films, and regenerated cellulose spheres. It was found that the
hydrophobicity of the cellulose surfaces increased with longer graft lengths, and
that polymer grafting rendered a smoother surface morphology.
To improve the grafting efficiency in the ROP from filter paper, both covalent
(bis(methylol)propionic acid, bis-MPA) and physical pretreatment (xyloglucanbisMPA)
were explored. The highest grafting efficiency was obtained with ROP
from the bis-MPA modified filter papers, which significantly increased amount
of polymer on the surface, i.e. the thickness of the grafted polymer layer.
MFC was grafted with PCL to different molecular weights. The dispersability in
non-polar solvent was obviously improved for the PCL grafted MFC, in
comparison to neat MFC, and the stability of the MFC suspensions was better
maintained with longer grafts.
PCL based biocomposites were prepared from neat MFC and PCL grafted MFC
with different graft lengths. The polymer grafting improved the mechanical
properties of the composites, and the best reinforcing effect was obtained when
PCL grafted MFC with the longest grafts were used as reinforcement.
A bilayer laminate consisting of PCL and MFC-films grafted with different PCL
graft lengths displayed a gradual increase in the interfacial adhesion with
increasing graft length.
The effect of grafting on the adhesion was also investigated via colloidal probe
atomic force microscopy at different temperatures and time in contact. A
significant improvement in the adhesion was observed after polymer grafting.
School:Kungliga Tekniska högskolan
Source Type:Doctoral Dissertation
Keywords:MEDICINE; Chemistry; cellulose; ring-opening polymerization; polycaprolactone; grafting from
Date of Publication:01/01/2009